Method of manufacturing pressure sensitive imaging materials

ABSTRACT

A pressure sensitive, reusable, long lasting, and substantially smudge free imaging material and method of making same comprising an integral film having a color yielding lyophobic dispersion of pigmented substance in a plasticizer at the bottom of the film and one synthetic polymer in the form of a resinous binder at the top of said film and having a multitude of minute capillary openings serving as a reservoir for said color yielding substance and for permitting said color yielding substance to be pressed out onto an adjacent image receptor.

Q United States Patent 11 1 1111 3,895,130

Barouh et a1. July 15, 1975 [54] METHOD OF MANUFACTURING 3,274,089 9/1966 Wolinski 117/93.1 CD 3,287,153 11/1966 Schwarz et a1 l17/36.1 fi gi ggfi ig IMAGING 3,413,184 11/1968 Findlay et a1. ll7/36.1 X 3,552,990 1/1971 Barouh 117/36.l [76] Inventors: Victor Barouh, 935 Plum Tree Rd. 3,628,979 /1 Newman 8t fi ll7/36.4 We t We tbu -y N York 11590; 3,682,764 8/1972 Findlay et a1. 161/160 Sylvester Giaccone, 95-05 59th Ave., Flushing, New York 11373; Primary Examiner-Thomas J. Herbert, Jr. Robert Glenn, 70-20 108th St., Attorney, Agent, or Firm-Kenneth S. Goldfarb Forest Hills, New York 11375 [22] Filed: Nov. 12, 1973 [57] ABSTRACT [21] Appl. No.: 414,917 A pressure sensitive, reusable, long lasting, and substantially smudge free imaging material and method of Related Apphcauon Data making same comprising an integral film having a [62] of 26617051111 1972- color yielding lyophobic dispersion of pigmented substance in a plasticizer at the bottom of the film and [52] [1.5. Cl. 427/152; 427/153; 282/28; one Synthetic polymer in the f of a resinous binder 428/307 at the top of said film and having a multitude of min- [51] Illt. Cl. B41C 1/06 ute capillary Openings Serving as a reservoir for said [58] Field of Search ll7/36.1, 36.4, 93.1 CD, c0101. yielding substance and for permitting Said c0101. 47 H; 161/160 yielding substance to be pressed out onto an adjacent image receptor. [56] References Cited UNITED STATES PATENTS 3/1959 Nelson et a1 117/47 10 Claims, N0 Drawings METHOD OF MANUFACTURING PRESSURE SENSITIVE IMAGING MATERIALS RELATED APPLICATION This application is a division of the application of Victor Barouh, Robert Glenn, and Sylvester Giaccone, Ser. No. 266,705, filed June 27, 1972, Group 167, for PRESSURE SENSITIVE IMAGING MATERIALS AND METHOD OF MANUFACTURING.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pressure sensitive imaging material that may be used in lieu of reusable sheets of carbon paper, in lieu of reusable, single chrome office and data processing machines and in lieu of reusable bi-, or multi chrome office machine ribbons.

2. Description of the Prior Art Up to the present time the most widely used types of carbon paper consist of a supporting, fibrous tissue base onto which is applied a mixture of waxes, oils and color yielding pigments and/or dyes. Upon application of type, or stylus pressure, a portion of that mixture is transferred to an adjacent surface of paper or other image receiving material.

Such sheets of conventional carbon paper have the following disadvantages:

l. The amount of waxy composition that can be applied to a thin tissue paper is limited because of the inherent brittleness and lack of cohesiveness of such compositions that flake off their supporting base if applied in too thick a layer.

2. The thin tissue paper necessary for good copy and manifolding is easily damaged by the impact of types or by stylus pressure.

3. The transferred, image producing portion of the waxy ink composition remains on the surface and does not penetrate into the fibers of an adjacent image receptor. From there it is easily wiped off during handling, thus rendering the copy unclear and smeary.

The most common reusable office and data processing machine ribbons now in use, consist of inked woven fabrics, such as cotton, silk and synthetics. A liquid ink of non-drying oils, dyes and/or pigments is carried in, and absorbed by the capillary pores of the yarn and the open spaces between the individual threads. Such reusable inked ribbons have the following disadvantages:

1. Due to the thickness of the woven fabric (0.004 to 0.005 inch a sharp image of good definition, essential in offset work and for optical character recognition cannot be obtained.

2. The liquid ink with which the fabric is saturated easily offsets and stains the fingers of operators who must handle it.

3. Since ink is present on both sides of the ribbon, typefaces gradually pickup ink and loose fiber fragments, clogging up the type fonts. Images produced by such clogged typefaces are of very poor definition.

Recently, there have come on the market improved, socalled solvent carbon sheets and office and data processing machine ribbons in which the image producing layer consists essentially of a plastic continuous phase with sponge like properties, thus permitting a thicker coating for greater durability, and a liquid, or semi-liquid discontinuous color yielding phase. The name solvent carbon derives from the face that before application the resin or plastic must first be dissolved in a suitable solvent which is subsequently evaporated. Since only the liquid color yielding phase, or ink, is transferred during use, that ink penetrates somewhat below the surface of an adjacent porous image receptor, thus yielding a cleaner copy.

While these new imaging materials show some advantages over conventional carbon paper sheets and inked ribbons, they also have the following essential deficiencies:

1. When left interleaved between sheets of copy receiving paper, the liquid, or semi-liquid ink, suspended within the spongy, resinous, image releasing layer, migrates and offsets onto that paper, leaving it stained and its own intensity much diminished.

2. The cleanliness of these products leaves much to be desired, because ink is discharged easily during handling.

3. Since the percentage of the resinous binder in these systems is rather low, usually between 25 and 30 percent of the dry weight, the transfer layers are of poor strength and cannot withstand for long the repeated impact of types, or stylus.

To overcome the latter weakness, some, such imaging materials use various nonfibrous films as the supporting base instead of tissue paper. But even such films have found only limited use as reusable office machine ribbons, since many of the typewriters in general use have typefaces of such sharp configuration, that they cut, or stencil through even a very strong supporting base film, causing it to tear. Moreover, because of the manner of manufacturing these imaging films, bichrome ribbons are not practicable to produce and were in fact never marketed on any appreciable scale.

SUMMARY OF THE INVENTION Accordingly, it is the object of the present invention to provide imaging materials and methods for their production that overcome the above enumerated deficiencies.

It is a further object of the invention to provide a pressure sensitive, long lasting and substantially smudge-free imaging material and method of producing imaging material to be used in lieu of conventional reusable carbon paper and the like, in lieu of single chrome office and data processing machine ribbons and in lieu of bior multi-chrome office machine ribbons. The imaging material comprises the concept of applying a priming layer to a flexible supporting base, then applying an imaging layer thereon, essentially of a color yielding lyophobic dispersion of pigments and- /or dyes in an oil or secondary plasticizer, concentrated at the bottom of said imaging layer and a resinous portion, consisting of one, or more plasticized, or unplasticized synthetic polymers, substantially concentrated at the top of the imaging layer and contained within that binder a multitude of minute capillary openings, serving as the reservoir for the color yielding portion and permitting the latter to be pressed out onto an adjacent image receptor by the application of stylus, or type pressure.

According to this invention, a suitable base paper, or nonfibrous film may be coated with a resinous priming layer, providing the imaging overlayer with a suitable adhesive working surface. Preferably such a resinous priming layer will also contain some primary plasticizer for the resin from 0.5 to 8 percent and from O to 40 percent of a coloring pigment. The purpose of the latter is to give the back face of the final product an appearance, distinctly pleasing and different from that of the imaging layer, in case a transparent film is used as the supporting base. Such a different appearance is not only of an esthetic value, but also serves to separate any finished product, where, through the oversight of the machine operator, the priming layer was omitted. During tests conducted to improve the appearance of nonfibrous imaging materials, by incorporating various pigments and metal powders into the priming layer, it was discovered that imaging layers applied to primers, containing from 25 to 55 parts per dry weight of a nonleafing metal powder, surprisingly showed significantly improved adhesion to such primers. It is theorized that this phenomenon is probably due to the fact, that nonleafing metal powders impart a greater free surface energy to the priming layer thereby improving both spreading and penetration of the imaging layer and therefore provide conditions for better bonding action.

One essential feature of the resinous binder of the priming layer, is that it must not be soluble in the plasticizers of the imaging layer, so as not to cause any diminishing of the image intensity, due to plasticizer migration into the priming layer.

Another essential feature of the prime coating is sufficient liquidity so that intimate contact between the coating and the working side of the supporting base can be achieved during application.

The necessary working viscosities can be obtained through one of the following methods:

I. Dilution by suitable thinners, which after application are driven off in a drying tunnel.

2. Heating the prime coating above the congealing point temperature of the resinous binder.

3. A combination of both methods.

Since most of the commercially available nonfibrous base materials have very smooth surfaces that are detrimental to good bonding, it is furthermore essential to provide a film surface of sufficient roughness in order to insure good bonding between the supporting substrate and the bonding, liquid prime coating.

In one method of providing such nonfibrous base materials with a rough surface, the film is passed over a roller with an abrasive surface. The speed of that roller can be varied and also reversed. By varying the speed of the abrasive roller, its direction and the contact angle of the web, the degree of roughness can be varied within a wide range.

In an alternate method the working face of the nonfibrous base film is subjected to a corona discharge treatment. Such a treatment also assures sufficient roughness of the working surface of a thermoplastic base material, so that it greatly facilitates penetration and spreading of the prime coating and thus creates favorable conditions for good bonding action.

In a preferred method of application, the prime coating is first premetered onto a roller, revolving at exactly the line speed. The base material is squeezed onto this roller by an impression roller in contact with the back face of the web. The purpose of this squeezing pressure, which can be varied to suit differing conditions, is to enhance penetration and spreading of the prime coat. By employing this application method, most, but not all, of the premetered prime coating is transferred to the web. Some of the coating material remains on the applicator roller, thereby creating a split film condition at the coating/applicator roller interface. In this manner minute kiss or screen marks are created on the priming layer, thereby providing an artificial rough surface for the subsequent casting of the imaging layer. Of course, the flow, drying and/or congealing conditions of the coating, immediately following its application,

have to be such, that a leveling action of the still liquid coating cannot take place, so that the surface roughness is left intact, even after the coating has been cured.

In still another embodiment of the present invention the resinous prime layer is chosen from thermoplastic resins having good flow properties at elevated temperatures. When the prime coating is applied by the method just described, a thermoplastic film base will slightly melt at the coating interface, thereby fusing with the primer and creating a very satisfactory bond, even when such difficult to adhere to materials as the polyolefin films are used as the supporting substrate.

In another fusing method, a thermoplastic primer can be chosen from among aqueous resin dispersions. After the water is evaporated by force drying, the coated base film is exposed to infrared heat radiation of sufficient intensity to fuse the priming layer to the base film.

In still another embodiment of the present invention, and especially where great film strength is desired, the resinous priming binder is chosen from thermosetting, or chemically crosslinking resins that will provide good impact resistance to the finished product, while still adhering satisfactorily to both the supporting and the imaging substrate.

Representative compositions for the priming layer are the following:

Thermoplastic Hot Melt Type:

40 parts Polyvinyl acetate-polyethylene copolymer 15 do. Polyisobutylene 25 do. how molecular polyethylene 10 do. Castor wax 10 do. Parafiine 100 parts Example III Hot Melt Curing Type:

25 parts G.E. -100 Phenolic resin 25 parts Triphenyl phosphate 10 parts Staybelite ester 10 20 parts Polyvinyl acetal 20 parts Castor wax parts Example IV Thermoplastic Emulsion Type -Continued Example IV 50 parts Acrylic ester resin emulsion (nonionic) 7 parts Methanol '10 parts Phtalocyamine Blue 25 parts Titanium Dioxide 5 parts Thamol 731 Dispersing and Stabilizing agent 3 parts Triton CF 10, non-ionic surfectant 100 parts Example V l 100 parts The imaging layer of the present invention consists of a resinous binder dissolved in certain solvents, certain finely dispersed pigments and/or dyes, certain oils, serving as the vehicle for the color yielding ingredients, and, if necessary certain primary plasticizers.

The following relationships between the various ingredients of the imaging layer are essential features of the present invention:

1. The solvent system must contain at least one low boiling primary solvent and one secondary higher boiling solvent.

2. The high boiling solvent should not exceed 25 percent by weight of the low boiling solvent.

3. The low boiling solvent must not form an azeotropic mixture with the high boiler, or must do so only to a very limited extent.

4. The low boiling solvent must have preferential solvent power for the resinous binder and the primary plasticizer.

5. The secondary plasticizer(s), or oils together with the pigments and/or dyes must form a lyophobic dispersion within and somewhat below the surface of the resinous binder.

Where as it has been common in prior art to limit the ratio of the binder to the incompatible, color yielding portion of the system to approximately 1 3, it is possible, according to the present invention to increase this ratio to as much as 2.5 1. This is accomplished in the following manner:

A supporting substrate of paper of film which may, or may not be prime coated in the previously described manner, but which in the case of such a substrate being a film with a prime coating, has undergone a corona treatment, after the application of the prime coating, is coated with a mixture of solvents, binder, plasticizer, and pigment, and/or dye. As the low boiling solvents evaporate inside a suitable drying tunnel, by reason of their greater solvent power for the binder system, they cause a major portion of that binder to be carried towards the free surface where a continuous film is formed. Upon further heating, the high boiling secondary solvents are driven off, through that film, leaving a so-called blushed surface, consisting of a multitude of capillary size openings in that film. Not only can the liquid color yielding phase underneath be pressed out of these capillary openings through stylus, or type pressure, very similar to the way an ink is squeezed out of an ordinary fabric ribbon, but the surface also changes its color to a much lighter hue than the one provided by the under laying. pigments. This is due to the fact that the initial transparency of the film formed on the free surface by the evaporation of the low boiling solvents, is destroyed by the subsequent evaporation of the high boiling solvents and the formation of the capillaries. Thus it is possible to obtain a black, or deeply colored image from a color releasing media whose face may actually be white. Even though, the free, blushed surface of the new product will gradually darken during use, it will still be far cleaner and more durable than any similar product, known before because of its greater resin content.

Representative examples of the casting composition for the imaging layer are the following:

Example VI 100 parts Example V11 12 parts Hard acrylic resin acryloid A-ll 5 parts Tricresyl phosphate primary plasticizer 7 parts Monoplex S- incompatible plasticizer 6 parts Carbon black 2 parts Methyl violet 58 parts Methyl Ethyl Ketone low boiling primary solvent 10 parts lsobutanol high boiling secondary solvent parts Example VIII 1 1 parts Polyvinyl acetal Butvar B98 2 do. Santicizer 141 primary plasticizer 7 do. Rape seed oil incompatible plasticizer 6 do. Toluidene red 68 do. Chlorofonn low boiling primary solvent 6 do. Xylene high boiling secondary solvent 100 parts Example 1X 10 parts A.B.S. Polycarbonate Cycoloy 800 6 do. Monoplex 71 primary plasticizer 8 do. Butyl Stearate incompatible plasticizer 5 do. Carbon Black 1 do. Molybdate blue toner 62 do. Methylenchloride low boiling primary solvent 8 do. lsobutanol high boiling secondary solvent 100 parts Example X 17 pans Cellulose acetate 9 do. Dioctyl sebacate incompatible plasticizer 7 do. Alkali blue -Continued Example X 60 do. Ethyl acetate low boiling primary solvent 7 do. V M & P naphta secondary high boiling solvent 100 parts If it is desired to produce an extra thin imaging film Example Xlll l l parts Polyvinyl Acetal Formvar /95 3 do. Primary plasticizer Paraplex G 54 86 do. Trichlorethylene 100 parts By still another method and also within the scope of for extra Sharp images and extra yardage that can be 10 the present invention, it is further possible to produce wound on an office machine spool or core, it is possible to cast a coating composition, such as one given in the foregoing examples, but likely to contain an even greater percentage of resinous binder, on a previously untreated film base of polyolefin, or other substrate with good release properties and subsequently after curing, or drying separate the two webs by stripping and rewinding each on a separate reel. The now selfsupporting film can then be cut and rewound on various office machine spools, while the supporting web may be used many times over, for repeated castings.

Contrary to previously known imaging films of this type with their relative low binder content, selfsupporting films, obtained by this novel process have far greater tensile strength and impact resistance. Moreover their ink carrying capacity is also considerably larger because the capillaries within the film are able to retain or absorb a far greater amount of a more liquid ink for longer wear and improved penetration into the image receptor sheet.

It is also possible to cast a second overlayer on top of a self-supporting imaging layer before stripping. For this purpose a resin can be selected that will impart still greater strength and flexibility to the product. The surface of the film thus becomes sealed and ink can no longer be released through it. Since the obverse side which is the side having initially faced the supporting base film, with its greater ink concentration, now be comes the imaging side, products made according to this method, by reason of the greater smudginess of that face, are not particularly suitable for use as carbon paper sheets because of the close contact such sheets have during use, with the adjacent copy paper. However their use as an office machine ribbon is ideal, since typefaces coming in contact only with the clean face, do not pick up ink and remain clean indefinitely.

Successful reinforcing backings were cast from the following solutions:

an imaging material, as described, with a supporting base of nonfibrous materials, such poly propylene, polyterephtalate, polycarbonate, poly vinyl chloride nylon and the like, with a priming and an imaging layer and then laminate another, different kind of film to the back face of the supporting base film. in this manner, the most desirable properties of 'a supporting base, such as tensile strength, impact resistance, toughness and flexibility that previously were always mutually exclusive properties in a single base film can conveniently be combined. Most preferably, the thickness of such backings, as well as that of the supporting base film will vary between 0.00025 and 0.0012 inches for a total thickness of the laminated imaging material of0.00 l to 0.003 inches. I

The just described method of providing a reinforced backing to the original base film is especially advantageous when it is desired to produce bi-chrome office machine ribbons. In this case, the original imaging material with only one supporting base film of, formstance, 0.0005 inch thickness, tensilized, polyester film is cut into narrow tapes of a little less than one half the width of the end product. Another reel of like material, but of different color. is cut in the same manner. Two narrow tapes of differing color are then laminated along side each other on a full width' backing tape of say 0.001 inch thick, biaxially oriented, high density polypropylene film. The laminating adhesive should most preferably be of the crosslinking type, that will not only assure a permanent bond between the two films, but also contributes to the products strength and impact resistance. Two laminating compositions that were found to perform well on two such films that had undergone a corona discharge treatment on their working surfaces, just prior to laminating are the following:

Formulas used to laminate ribbons to make a Bi-chrome Ribbon Example Xl Example XIV I 12 parts Cycoly 800, A.B.S.-polycarbonate alloy 9 Parts A y Q y i A ll 2 do. Primary plasticizer (Paraplex G 54) 6 Polyvinyl chloride P! 40 do. Dichloro ethane 55 $2g|i+nyl resin 28 do Methylene Chic 6 V 5 do. Urea formaldehyde resin Uformite F v 240 18 do. Toluene 10 do. Methyl cellosolve I00 parts 70 do. Methyl ethyl ketone [00 parts Example Xll l4 parts A.B.S. resin (Acrylo nitrile butadiene Example xv V 40 d T l styrene copolymer) 8 parts Epon 1000 epoxy resin 0 o. o uene 8 d 36 do. Tnchlorethylene 52 3 x ii fif y' g go Yes!" parts 32 do. Toluol 100 parts From the foregoing description it should be evident that other materials may be substituted for the various layers and supporting substrates. The important aspect of the invention is the physical makeup of the various layers and their relationship to each other, as well as to the supporting substrates. Obviously there are a wide variety of resins, plasticizers, oils, pigments and dyes that can be used to attain the same results. Also, since new materials always appear on the market, many of those will be adaptable to this invention. The examples given should therefore not be regarded as all inclusive, or limitative of the following claims.

We claim:

, l. A method of making a pressure sensitive, reusable long lasting substantially smudge free imaging material comprising the steps of (1) coating a substrate base with a layer-forming composition of resinous binder containing up to 8 percent of plasticizer and up to 40 percent of pigment to form a priming layer on said base, (2) coating said priming layer with an imaging layer-forming composition comprising (A) resinous binder dissolved in a non-azeotropic mixture of low boiling solvent and high boiling solvent, said low boiling solvent having preferential solvent power for said resinous binder, the amount of said high boiling solvent not exceeding about 25 percent by weight of said low boiling solvent and (B) a color yielding lyophobic dispersion of finely divided pigment and/or dye and (3) heating to evaporate off said low boiling solvent whereby a major portion of the resinous binder is carried toward the outer surface of said imaging layer to form a film thereat, heating to evaporate off said high boiling solvent to form openings in said film.

2. A method of making a pressure sensitive imaging material according to claim 1, in which a surface of said substrate is subjected to a mechanical treatment by an abrasive roller.

3. A method of making a pressure sensitive imaging material according to claim 1, in which the major ingredient of said priming layer is selected from either a thermosetting or crosslinking resin.

4. A method of making a pressure sensitive imaging material according to claim 1, in which said priming layer is of a thermoplastic resin of low melt viscosity and is kiss imprinted on said substrate.

5. A method of making a pressure sensitive imaging material according to claim 1, in which the working surface of said priming layer is subjected to a mechanical treatment by an abrasive roller just prior to coating of the imaging layer.

6. A method of making a pressure sensitive imaging material according to claim 1, including the further steps of striping said film off said base after said solvents have substantially evaporated so that said film is self-supporting.

7. A method of making a pressure sensitive, selfsupporting imaging material, according to claim 6, in which the proportion of said resinous binder to said lyophobic dispersion of pigmented substance is between l:l and 2:1 by weight.

8. A method of making a pressure sensitive, selfsupporting imaging material, according to claim 6, wherein there is cast, before stripping a reinforcing resinous overlaying film that effectively seals that surface against release of said color yielding substance, said sealed surface becoming the obverse side of the finished product.

9. A method of making a pressure sensitive imaging material according to claim 1, wherein after substantial evaporation of said solvents said imaging layer is exposed to infrared heat of a temperature just high enough to permanently fuse said priming layer to said substrate.

10. A method of making a pressure sensitive imaging material according to claim 1, wherein said low boiling primary solvent is selected from toluene, methyl ethyl ketone, chloroform, methylenchloride and ethyl acetate. 

1. A METHOD OF MAKING A PRESSURE SENSITIVE, REUSABLE LONG LASTING SUBSTANTIALLY SMUDGE FREE IMAGING MATERIAL COMPRISING THE STEPS OF (1) COATING A SUBSTRATE BASE WITH A LAYER-FORMING COMPOSITION OF RESINOUS BINDER CONTAINING UP TO 8 PERCENT OF PLASTICIZER AND UP TO 40 PERCENT OF PIGMENT TO FORM A PRIMING LAYER ON SAID BASE, (2) COATING SAID PRIMING LAYER WITH AN IMAGING LAYER-FORMING COMPOSITION COMPRISING (A) RESINOUS BINDER DISSOLVED IN A NON-AZEOTROPIC MIXTURE OF LOW BOILING SOLVENT AND HIGH BOILING SOLVENT, SAID LOW BOILING SOLVIENT HAVING PREFERENTIAL SOLVETPOWER FOR SAID RESINOUS BINDER, TE AMOUNT OF SAID HIGH BOILING SOLVENT NOT EXCEEDING ABOUT 25 PERCENT BY WEIGHT OF SAID LOW BOILING SOLVENTAND (B) A COLOR YIELDING LYOPHOBIC DISPERSION OF FINELY DIVIDED PIGMENT AND/OR DYE AND (3) HEATING TO EVAPORATE OFF SAID LOW BOILING SOLVENT WHEREBY A MAJOR PORTION OF THE RESINOUS BINDER IS CARRIED TOWARD THE OUTER SURFACE OF SAID IMAGING LAYER TO FORM A FILM TEREAT, HEATING TO EVAPORATE OFF SAID HIGH BOILING SOLVENT TO FORM OPENINGS IN SAID FILM.
 2. A method of making a pressure sensitive imaging material according to claim 1, in which a surface of said substrate is subjected to a mechanical treatment by an abrasive roller.
 3. A method of making a pressure sensitive imaging material according to claim 1, in which the major ingredient of said priming layer is selected from either a thermosetting or crosslinking resin.
 4. A method of making a pressure sensitive imaging material according to claim 1, in which said priming layer is of a thermoplastic resin of low melt viscosity and is kiss imprinted on said substrate.
 5. A method oF making a pressure sensitive imaging material according to claim 1, in which the working surface of said priming layer is subjected to a mechanical treatment by an abrasive roller just prior to coating of the imaging layer.
 6. A method of making a pressure sensitive imaging material according to claim 1, including the further steps of striping said film off said base after said solvents have substantially evaporated so that said film is self-supporting.
 7. A method of making a pressure sensitive, self-supporting imaging material, according to claim 6, in which the proportion of said resinous binder to said lyophobic dispersion of pigmented substance is between 1:1 and 2:1 by weight.
 8. A method of making a pressure sensitive, self-supporting imaging material, according to claim 6, wherein there is cast, before stripping a reinforcing resinous overlaying film that effectively seals that surface against release of said color yielding substance, said sealed surface becoming the obverse side of the finished product.
 9. A method of making a pressure sensitive imaging material according to claim 1, wherein after substantial evaporation of said solvents said imaging layer is exposed to infrared heat of a temperature just high enough to permanently fuse said priming layer to said substrate.
 10. A method of making a pressure sensitive imaging material according to claim 1, wherein said low boiling primary solvent is selected from toluene, methyl ethyl ketone, chloroform, methylenchloride and ethyl acetate. 